When Flat Logo finds the colors itself (no colors named), a flat bar
two pixels wide (whole pixels of one color) on a ground beside other
art was lost or traced in another color. No bar pixel has a uniform
3 x 3 neighborhood, so neither the first clustering nor the check for
unexplained colors took it. A gray bar on white beside black art was
traced as white, and a red or green bar was traced as black. Bars
three pixels wide or more were already found.
The check for unexplained colors now also takes the pixels of such a
bar: two rows or columns of one color (within about 3.5 in RGB
distance), three pixels long, with the same ground on both sides. They
count when the known colors do not explain them, and also when their
color lies less than two thirds as far from the ground's known color
as from every other known color, where the bar would otherwise be
traced as the ground. A gray bar darker than about #9B9B9B on white
beside black art stays black, #808080 included, because a black stroke
1 to 1.6 px wide on the pixel grid gives the same pixels. Named colors
are unchanged.
The fit of a thin outline can lose all its area. Its two sides can
straighten onto one line, which leaves two anchors whose segments run
back and forth along it. Or the fit can be a single cubic, which becomes
one anchor and has no segment. Both occur when Flat Logo traces noise
whose cells are one pixel in size. The trace kept such an outline as a
selectable path that paints nothing.
Flat Logo now leaves out an outline whose area is below 1e-6 px^2,
together with its holes, and a hole whose area is below 1e-6 px^2. The
area is summed about the outline's first anchor, as the other trace
modes already do for a filled loop (crates/trace/src/lib.rs:996-1001).
Outlines with an area of 1e-6 px^2 or more, thin slivers included, are
kept as before.
One test traces a black and cream noise with both colors named exactly
and checks that no subpath of the result lacks an area. Two more build
shapes from straight cubics: a hole without area is left out, and an
outline without area is left out with its hole.
Flat Logo traces a copy of the image at most 1024 pixels on a side,
averaged down by a whole factor, so a 1025-pixel image is traced at
513 pixels. The trace's warnings did not say so, because they compared
the image only with the decoded raster. For an image over 1500 pixels
they said instead that it is traced more slowly, which Flat Logo does
not do.
The trace result now carries Flat Logo's working size when it averaged
the image down. imageTrace.make and imageTrace.makeAndExpand then name
both sizes in their warnings, and the status bar shows that note, in
place of the slower-trace and megapixel notes. Other modes keep their
warnings. The message has a row in each catalog that translates the
other Image Trace warnings.
Found while testing crates/trace/src/logo/palette.rs:9-15 (parse_hex)
Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Auto Grouping compared the box of every traced path with the box of every
path that can hold something, and with Overlapping it also compared each
grouped path with every path below it. On a 1400 x 1400 px noise image
traced with Limited 8, Overlapping (18,653 paths), parents() made
442,998,298 box tests and took 3.0 s in a release build.
parents() now keeps the holders and, for stacked traces, the paths below in
a grid of about one cell per path. A path's candidates are the holders in the
cell of its box center, smallest first, and the paths below it come from the
cells its box reaches. When a box reaches more cells or entries than there
are paths below it, the old scan is used. The cells grow larger when the
boxes would otherwise be listed in more than 32 cells each on average. The
same trace now takes 142,289 box tests and 0.08 s, and every parent is the
same as before. The 20,000-path limit is unchanged.
The tests compare parents() with the pairwise version on rings, faces and
noise traced Abutting and Overlapping, check that a dense trace takes at most
64 box tests per path while the pairwise version takes more, check that 300
nested discs take no more box tests than the pairwise version, and check
that boxes covering the whole image make the cells larger.
A pixel on the edge of a cut-out image with an alpha of 128 or more was
traced with its own color. When that color was a darkened edge tone, it
took whichever palette color lay nearest, and the edge traced as 1 px
slivers of a color that appears nowhere near it.
In Color and Grayscale, a pixel with an alpha of 128 to 254 next to a
pixel under half opaque now takes a color of the fully opaque pixels
within two pixels of it when its own color is that color or a darker
shade of it, counting only pixels it reaches without crossing a
transparent gap; of several such colors, it takes the one the most of
those pixels have. It keeps its own color when one of those pixels has
it, or when its color is not a shade of any of theirs, so a thin
semi-transparent outline of another color stays as it is. Ties go to the color nearest its own, by its gray
in Grayscale. Opaque images trace as before.
Fitting straightens the pieces of an outline that lie close to a line, and
Snap Curves To Lines straightens more of them. The outline of a single
pixel, or of a region one pixel thick along an edge such as an opaque row
of a mid tone under a light shape, can then have all its pieces on one
line. The trace held a selectable path with no area, for example a path
140 x 0 px with Snap Curves To Lines.
In a Color, Grayscale or Black and White trace with Fills, a fitted
outline or hole whose area is below 1e-6 px^2 is now left out. A path
with no area paints nothing, so the traced result paints the same pixels
as before. Without Fills, the 1 px stroke that outlines each area draws
such a loop, so it is kept. A single closed loop keeps its area as
before.
The Automatic palette counts flat art's colours by area (a colour needs
about 1% of the picture, 0.5% at Colors 100) and fits that count with
median cut and area-weighted k-means. A stem, a highlight, or a near
white beside a pale background (within 24 levels, so in one box) was
averaged into a large neighbour; mixed-colour merging and Noise could
then remove what was left.
On the flat route only, after the count is fitted, rare_colours finds
the colours too rare or too close for it and keeps those that are
distinct (at least 2.5 in Oklab x 100 from every palette colour and from
the main colour each stands for), flat (mostly one histogram bin) and
drawn (a 4-connected region of their own unblended pixels of at least 8
pixels, or three of at least 4); a colour lying between two others, as
anti-aliasing mixes them, must also have an inside. At most six, largest
region first. They stay fixed while the other colours are refitted
around them; merge_mixed leaves them alone; denoise_keeping keeps their
regions of 4 pixels or more whatever Noise is (smaller specks still go).
Full Tone, Limited and Automatic's continuous-tone route are unchanged,
and denoise without kept labels is as before.
Methods cited in the code: median cut (Heckbert 1982), k-means (Lloyd
1982), Oklab (Ottosson 2020), salient-colour preservation (Fukuda et al.
2019, doi:10.1117/12.2521607). The rule and its numbers are VectorCraft's
own; Adobe does not document how its palettes are chosen.
Tests (code-drawn): a rare stem or patch over 2-8 flat colours, hard
and anti-aliased at 1x and 2x; near-white highlights on #FFF4E0 kept and
still paths at Noise 16; a 3 px #909090 stem on #808080; scattered
single pixels of the same areas add no colour; denoise_keeping at Noise
0-32.
Measured on 66 synthetic flat logos (22 designs x hard 1x, anti-aliased
1x and 2x; local inputs): every key colour and no spurious one in 66
(was 39); missing key colours 0 (was 43), spurious 0 (was 2), merged
pairs 0 (was 46); rendered dE00 0.348 -> 0.138. Four public-domain scan
crops take the continuous-tone route and are unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
The public documentation says Image Trace warns about images larger
than 1500 pixels on a side but traces them, only more slowly. VectorCraft
traced them silently, and refused any trace of more than 2,000,000
anchors, which a 4000 x 3000 photo at High Fidelity Photo nearly reaches
(1.9 million on a code-drawn photo) and a noisier one passes.
- imageTrace.make and makeAndExpand return `warnings`: one for an image
over 1500 px on a side (traced, but more slowly; a lower-fidelity
preset or a smaller copy is quicker), one for an image over 64 MP
that was traced from a scaled-down copy. The app shows the first in
the status bar.
- MAX_TRACE_ANCHORS is 8,000,000 natively (2,000,000 on wasm, where a
page has at most 4 GB). Measured through imageTrace.make on
code-drawn photos: about 90 bytes an anchor kept in the document;
7.9 million anchors kept 685 MB with an 876 MB peak (4000 x 3000,
Full Tone at Colors 100, Paths 100, Noise 1, 37 s).
- The refusal keeps its translated advice: raise Noise, lower Paths or
Colors, or pick a lower-fidelity preset.
Tests: a_large_image_traces_with_a_warning (1600 x 40 and 1500 x 8
code-drawn images, make and make-and-expand),
trace_warnings_name_a_large_or_scaled_down_image, a compile-time check
of the limit's range, and a UI test that the status bar shows the note.
Source:
https://helpx.adobe.com/illustrator/using/image-trace-results-optimization.html
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Raster::new checked its RGBA length with assert_eq!, so bytes of the
wrong length (from a file, a plug-in or a control message) would abort
instead of reporting an error. It now returns Result<Raster, TraceError>
and gives TraceError::Decode naming the byte count and the size (the
existing variant, whose text is already translated, instead of a new
message every language would need). The size product is checked for
overflow.
Raster::pixel indexed the bytes directly; it now gives transparent
black outside the raster, or past the end of a raster whose public
fields were set to a size its bytes don't have (which mosaic reads).
The public signature changes: every caller in the workspace was a test
(trace unit tests, Flat Logo tests and the quality harness), updated to
unwrap. No shipped code built a Raster with new; decode, decode_to_fit
and from_fn always make the right length, and trace_within already
refuses a raster whose fields disagree.
Test (code-drawn): a_raster_of_the_wrong_length_is_an_error_not_a_crash
(short, long, empty, zero-width and overflowing sizes; pixel, trace and
mosaic on a raster whose fields disagree).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Place junction clusters at their deepest pixel and prune terminal branches
by significance beyond their maximal discs. Merge overlapping junctions
and split crossings with continuing outer arms, then join degree-two runs.
Bound nodes, branches and simplification work, using checked data access.
Keep whole-blob selection, ink refinement, cap detection and fitting rules.
Test junction degrees, crossings, 24-angle lines, pruning, graph caps and
random-blob determinism. Record improved junction degrees and remaining
spur and extra-junction limitations in the centre-lines measurements.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: OpenAI <noreply@openai.com>
Compute exact squared Euclidean distances per blob with separable parabola
lower envelopes. Thin with bounded Guo–Hall active sets and retain diagonal
ends during staircase cleanup. Keep the whole-blob width rule and existing
graph, ink, cap and fitting rules, with checked access in the moved module.
Verify EDT against brute force, active sets against plain rounds, and both
diagonal slopes for length and connectivity. Record the centre-lines rerun
and its remaining limitations without changing feature scores.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: OpenAI <noreply@openai.com>
Measure Create Strokes on exact code-drawn scenes in aa and hard variants,
including centre/width error, topology, ends, spurs and painted coverage.
Keep the existing allocator report in one ignored test and document the
current baseline without changing tracing behaviour or dependencies.
Co-Authored-By: Codex <noreply@openai.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A small closed loop whose fit collapsed to a single cubic (fit_closed),
or a piece returning to its own junction with fewer than two fitted
cubics (fit_piece), kept every positioned point as a straight segment.
A looser Paths collapses more loops, so it could give more segments
than a tighter one.
Such a loop now tries the fewest segments that still hold it, each only
if the result keeps an area (more than 0.25 px^2) and stays within
1.5 * max(tolerance, 0.5 px) of the points both ways: the fit at up to
three somewhat tighter tolerances (what a slightly higher Paths gives);
for a closed loop then two cubics split at its start and its farthest
point, then the outline simplified at the tolerance and finer. The
positioned points stay the last resort, as before.
Test (code-drawn): a_higher_paths_never_gives_fewer_segments sweeps
Paths 0/25/50/75/100 over 32 seeded 48 px images of soft blobs plus
pixel noise in Color and Black and White at Noise 1 and 3. Before, six
runs had fewer segments at a higher Paths (e.g. 125 -> 79 from Paths 0
to 25); after, none. One image (seed 16, Black and White: 140 -> 136
from Paths 0 to 25, with or without this change) has another cause and
is left out of the sweep.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Where the pixel at a sharp corner falls to the other colour, the outline
cuts the corner in two one-pixel steps, and between two straight edges
of three cracks or more subpixel::outline makes those steps one point
(a notch). Whether the edges were long enough was measured on the whole
loop. An edge can run on past a junction in one region's loop while
the region across it, whose loop turns at that junction, sees a shorter
edge: one side made the notch and the other did not, so the shared
piece got different points on each side and the abutting curves left a
gap.
The notch now also requires the three cracks of each edge next to it to
lie in the piece (no junction among them), as the corner-pixel shift
correction above it already does.
Test (code-drawn): noisy_colour_images_leave_no_sample_uncovered traces
20 seeded 36 px images of soft overlapping blobs in four colours plus
pixel noise (Color, 5 colours, Noise 1 and 2, Paths 0/50/100) and needs
every one of five sample points per pixel to lie in some path: 93
uncovered before (seeds 9, 11, 13), 0 after.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Layers::shift read a crack's sub-pixel shift from its inside pixel,
looking for a thin run on the inside before one on the outside. Where
both sides are thin (a one- or two-pixel sliver beside another, as in
soft gradients and noisy scans) the two regions of the crack got
different shifts, so their shared piece got different points and the
abutting curves left slivers that no path covers.
The shift is now the mean of the readings from both sides,
(s(c) - s(c flipped)) / 2, which is exactly antisymmetric in floating
point (Crack::flipped gives the crack seen from its other side).
Tests (code-drawn images):
- a_crack_between_thin_slivers_has_the_same_shift_from_either_side:
every crack's shift is the exact negative of its flipped crack's, on
a noisy ripple of 1-2 px columns at three thresholds.
- shared_boundaries::thin_slivers_on_both_sides_of_an_edge_leave_nothing_uncovered:
a 48 px noisy ripple in Black and White at thresholds 140/157/170 and
Paths 0/50/100, sampled on the shared-boundary check's 4x4 grid per
pixel: 482-1,228 uncovered points per trace before, 0 after.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
With Method Abutting and Shapes on, a region recognised as a shape had its
outline replaced by the exact shape, but the region across that edge kept
its fitted curve unless it was a hole filled by one colour, and even then
the hole was recognised on its own, with its region's combined hardness.
A shape touching a junction (a third colour, or its own colour at a
corner) or the image's border was replaced on one side only, so abutting
colours parted or overlapped along the shared edge, and a square on the
image's corner could reach past the frame.
Cause: Layers::layer recognised an island with no holes
(`[only] => shapes::recognise`) regardless of what lay around it, and a
hole only by `one_colour_within`, each from its own outline and hardness.
Fix: under Abutting a shape is applied only where both faces take it
(`Layers::shared_shape`): the loop has no junction on it and does not
touch the border, the island has no holes and the hole holds one colour,
and the shape stays inside the image. The shape is recognised from the
outline turned one way and started at its leftmost anchor, with that
loop's own hardness, so the island and the hole it fills get the very same
shape. Overlapping is unchanged.
Test: shapes_keep_abutting_neighbours_watertight traces three code-drawn
anti-aliased colour images (a disc in a square plus a disc across its
edge, shapes on the border, tilted tiles) and checks every outline lies
within 0.001 px of a neighbour and a 4 x 4 per-pixel grid is covered
exactly once. Before: gaps of 0.50, 15.1 and 0.73 px, 183 and 276 points
uncovered or doubled; after: 0 px, 0 points. Isolated shapes are still
recognised.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Flat Logo found its colours only from solid pixels (a uniform 3 x 3
neighbourhood). Line art on paper has no solid area but the paper's: a
stroke one or two pixels wide never fills one, so its colour was a handful
of pixels among tens of thousands of white and was cut as noise (under
0.1% of the solid pixels). The palette came back empty and trace_logo
returned an empty TraceResult, which imageTrace.make reported as a success
with paths 0, anchors 0, colors 0.
Cause: logo::palette::auto_palette had no way to find a colour that has no
solid area, and logo::pipeline::trace_logo treats an empty palette as
nothing to trace.
Fix: when the solid pixels give no colour but white, auto_palette reads
the colours from the strokes' cores instead (line_art_palette): the opaque
ink pixels at least as far from white as each of their four neighbours,
the middle of each stroke where it is least blended with the paper.
Two guards keep that fallback to line art:
- Ink is a colour at least 48 below white in one channel, and the page
must have ink on at least 1% of its opaque pixels. Light grain and a few
sparse marks on otherwise blank paper stay blank, as plain white does.
- The lighter shades along a stroke's anti-aliased edge are local maxima
of their own; a colour that lies on the line from white to a darker
colour of the palette (within 20) is a blend of that ink with the paper
and is folded into it (fold_fringes), the ink keeping its colour.
The rest of the pipeline (unmixing, the flat-colour check and its NotFlat
refusal) is unchanged, and images with a solid colour other than white
never reach the fallback.
Tests (code-drawn inputs):
- thin_line_art_on_paper_is_traced_not_blank: four 2.4 px dark strokes
and two red marks on white. Before: palette [], no paths. After: dark
and red paths along the middle of every stroke and mark.
- anti_aliased_coloured_lettering_has_only_its_inks: rings, slants and
bars 1.6 px wide in red, blue and green. Without the fold: six colours
besides white; after: exactly the three inks.
- sparse_marks_on_paper_are_not_promoted_to_colours: 24 grey 12 x 2 px
marks of 239, 223 or 191 on a 256 x 256 page (under 1% ink). Without
the guard: palette [white, #efefef]; after: empty palette, no paths.
- grainy_blank_paper_has_no_ink: paper grain 243-255 traces to nothing.
- edge_shades_fold_into_their_ink_and_other_colours_stay (unit).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
contour::trace_mask built a table of outgoing directions for every
pixel corner in a raster pass and then followed it. It now works out
each turn during the walk from the two pixels ahead of the current
corner: right if the one ahead on the right is outside, straight if the
one ahead on the left is, else left (so at a saddle it still turns
right and diagonal pixels stay apart). Loop starts are found by
scanning the pixels for a top edge on the outline, with one flag per
pixel for a top edge already walked. The walk is bounded by the grid
size, and a mask of the wrong length now gives no loops instead of
failing an assert_eq!.
The output is identical: the_walk_equals_the_stored_direction_walk
compares it with a test-only copy of the previous walk on all 65,536
4x4 masks and 400 seeded 23x17 masks.
Time (best of 7, release, 4 cores): the walk alone on 2000x2000 masks
19.1 vs 26.6 ms (smooth pattern), 81.3 vs 93.2 ms (12% random pixels),
223.1 vs 238.1 ms (50% random); whole 1000x1000 traces 73.1 vs 77.1 ms
(Black and White), 249.6 vs 251.7 ms (Color, 6 colours), 214.1 vs
218.6 ms (Color, 6 colours, Noise 1), same segment counts.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
In Grayscale mode with Gradients on, the trace could fill paths with
coloured linear gradients (for example a blue-to-orange ramp) beside
grey flat fills. Gradient detection ran on the RGB image, so the stops
and the gradient's palette colour (its middle) were the source colours,
while Grayscale's flat fills come from each pixel's luma.
Grayscale now finds gradients, and settles their edges, in a copy of the
image reduced to the same Rec. 601 luma the flat grays are quantised
from. Every channel of that copy is equal, so the fitted stops, the ends
carried to the area's edges and the palette entry are all grey. Color
mode is unchanged: it still detects on the RGB image (trace output for
gradient fixtures is byte-identical before and after).
Adds grayscale_gradients_are_grey: a code-drawn sky ramp over flat
shapes with a ramp rectangle, traced in Grayscale with 4 grays and
Gradients on, must still produce a gradient, and every path colour,
gradient stop and palette entry must be grey.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Abutting traces must draw each edge between two neighbouring regions once:
the filled paths on either side follow one curve, one of them reversed, and
together cover the image without gaps or overlaps. These tests check that
from the trace output alone, with no renderer: points along each path's
outline must lie within 0.001 px of another path's outline, the paths' areas
must sum to the image's, and every point of a 4 x 4 per-pixel grid must lie
in exactly one path.
The images are drawn in code, hard-edged and anti-aliased, and traced in
Color (Abutting) and Black and White, each at the default settings, Paths and
Corners 0 and 100, Snap Curves To Lines, and Shapes. They cover a closed island
in a background, a ring with and without a core of a third colour, a wavy
two-colour seam, a three-region junction, outlines that leave a junction and
return to it (the 111 / 101 / 110 pattern at 1, 2, 3 and 6 px, and framed),
squares touching at a corner, a one-pixel hole and a one-pixel island (kept at
Noise 1, dropped together with what they leave at Noise 25), separate areas of
one colour, and slanted hatches with one-pixel paper channels. A further test
shows the check finds a 0.01 px shift and stacked (Overlapping) layers.
Two tests are ignored as documented current gaps:
- At Paths 0 and Corners 0, a piece returning to its own junction collapses:
its region is dropped and its area left uncovered (draft #2205 fixes it).
- With Shapes, a region whose outline runs through a junction becomes an exact
shape its neighbour does not share (up to 0.0039 px in Black and White).
No tracer code changes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
When a long horizontal or vertical run crosses a three-colour junction one
or two pixels before a corner, the corner correction for that run borrowed
a neighbouring crack's shift that the region on the other side of the
junction never applied, leaving hairline gaps between abutting colours.
The correction now applies only when all three cracks it uses lie in the
same shared piece.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tBcdwNhptqtmX32JCGFzB
Gradients (off unless asked for) found a blurred or noisy linear gradient in
part or in pieces, with bands around it.
The areas that may be a gradient are tried largest first, and one that is a
gradient is grown over every pixel next to it whose colour is within 10 levels
of the gradient's there: the pixels noise put a little off, a soft rim, the
pieces noise cut off it.
Linear-gradient inputs with Gradients on, paths beside the gradient, before ->
after: blurred 3.0 -> 0.5 (6 Colors) and 55.5 -> 0.5 (High Fidelity Photo);
noisy 11.0 -> 0.5 and 23.5 -> 1.5; scanned 5.5 -> 3.0 and 46.5 -> 37.0; clean
and aliased as before; dE within 0.02. No gradient on any input that is flat
colour, with any preset (the harness fails if there is one).
Each documented preset has an enhanced version (`enhanced: true` in
`imageTrace.make`, an Enhanced checkbox under the panel's preset): the preset
with Auto Grouping, and with Shapes in all but High Fidelity Photo. Gradients
stay an option. Flat Logo, a preset of our own, has none. The legacy presets,
and documents traced with them, are as they were.
So that an enhanced preset is no worse than its preset on that preset's inputs:
- A hole that one colour fills is the same shape as the path that fills it, so
the two still share one outline (a shape beside a fitted hole left slivers).
- A rectangle is as large as where its sides lie on average, not their farthest
points.
- Auto Grouping keeps the paths of a group in the order they were traced in. It
put a path first and what is inside it on top: a white counter traced under
its black letter was then painted over the letter's edge, a light seam
(Default with Auto Grouping, edge dE 10.24 -> 9.88; legacy 10.05).
The harness measures every enhanced preset beside its preset.
Create: Strokes drew every line with round caps: a square-ended line 10 px wide
had its corners 2.94 px outside the stroke.
- A line's ends are square when its ink reaches as far a third of the width to
either side of its middle as along it (a round end stops short there by a
seventh of the width); told from lines 3 px wide and more, all the ends of a
line together. The stroke then has square caps (`TracedPath::square_caps`).
- The last points of a wide line's skeleton can turn towards a corner of its
end. An end that has left the line the skeleton followed a width back (by a
quarter of the width, 1 px at least) is put back on it; and an end may be
pulled back as well as pushed out to where the ink ends.
Outline on the thin-line inputs: largest distance from the art 2.94 -> 0.88 px
(clean 2.94 -> 0.41; aliased 0.88 -> 0.81), mean 0.055 -> 0.050 px, anchors
14 -> 10.
- A sharp corner may fall up to 0.75 px short within 3 px of where it should be:
anti-aliasing and blur take that much off a corner (not on a thin bar, which
is all corners).
- A rounded rectangle gets the radius that fits its outline best, searched
around the one its area says, instead of that one alone.
- A rectangle's direction is tried along its longest straight side, the longer
axis of its area and the pixel grid: a blurred one may have no straight side.
- A regular polygon's sides, corners and size are read from the outline's shape
(how its distance from the middle goes round, and its area), not from how many
anchors the fitter gave it.
- An outline without anti-aliasing is known to half a pixel: it gets half as
much room again.
Plain shapes found with Shapes on, all sizes and variants: Default 57% -> 98%,
6 Colors 62% -> 100%. The harness counts false shapes: none on any input but one
thin line (a rectangle 2 px wide) whose trace is 0.70 px off with or without
Shapes.
A scan's paper is a tenth darker in one corner than in another. Flat Logo found
each tone of it as a colour of its own and traced the bands and the specks
between them: on the scanned inputs 470 paths, 21 px from the art on average.
Two palette colours are now one when the pixels between them are no fewer than
a third of those at the lesser of the two: flat colours leave only their shared
edge between them, tones of one colour fill the gap. Whether the image is flat
art at all is still asked of the tones as found.
Flat Logo on its inputs, all sizes and variants: 3.106 -> 0.090 px off on
average, 88.5 -> 0.82 px at most, 69.9 -> 3.9 paths; clean, aliased, blurred
and noisy art as before.
Snap Curves To Lines made every straight piece within 2.5 degrees of level or
upright exactly so, whatever its length: a 200 px line 2 degrees off had each end
moved 3.5 px. Now a piece is levelled only when neither end moves more than
1.6 px; a longer line that far off is left as the image has it.
Technical Drawing (the preset with the option on) on its inputs: largest
distance from the art 4.21 -> 1.46 px (1.43 before levelling existed), mean
0.178 -> 0.126 px; on the askew inputs 98% -> 70% of the outline comes out level
or upright.
Gradients (params `gradients`, a checkbox in the panel for Grayscale and Color;
off unless asked for): an area whose colour changes evenly along one direction
is traced as one path filled with a linear gradient, not as bands of flat colour.
Gradients are found before the palette is made, so no colour is spent on their
bands: a connected run of smoothly changing pixels is a gradient when a plane
fits each colour channel with all three sloping the same way, the colours along
that way are at most six stops with ramps between them, and painting them back
gives the area's own pixels. Flat colour, soft edges between flat colours and
shading that goes two ways are left as they were.
The harness gains two linear-gradient inputs with known lines and stops, and
measures whether each is found, the angle of its line and the colours of its ramp.
Auto Grouping (params `autoGrouping`, a checkbox in the panel; off unless asked
for): each traced path that has others inside its outer contour comes out in a
group with them, the path first, nested as deep as the picture is. The path that
covers the whole image is nobody's group.
The grouped result paints the same picture: where paths can overlap (stacked
layers, Flat Logo, strokes) a path only joins a path below it, and only if that
moves it under nothing that shares any of its box.
The harness measures three presets with the option on ("grouped %"), painting
them in the grouped order.
Shapes (params `shapes`, a checkbox in the panel; off unless asked for): a filled
outline that is a circle, an ellipse, a rectangle or a regular polygon comes out
as that live shape. A shape is only made when every point of the traced outline
lies within 0.5 px (0.2% of the shape's size, if more) of it; an ellipse whose
radii differ by less than twice that is a circle of its area.
The outline before fitting: a corner's own pixel no longer pulls the two edges
that meet there, and a one-pixel step between two long edges is the corner where
they meet. Sharp corners kept: Default 69% -> 76%, the colour presets 86% -> 91%.
The harness gains plain-shape inputs and "shapes %".
Create: Strokes (the Outline preset, or the option) traced lines along the pixel skeleton: right to a pixel,
with a width counted in pixels, and fitted by a separate, older fitter.
- Each skeleton point is moved to the middle of the line's ink, read from the image across the line: every
pixel counts as much ink as its colour is the line's rather than the paper's, the ink's centroid is the
middle and its sum the width (an anti-aliased or blurred line says both to a fraction of a pixel).
- The stroke width is the median of those widths, no longer a whole number of pixels.
- Each end goes where the ink ends, less the half width a round cap adds.
- Centre lines are fitted as outlines are: a straight line is two anchors, corners stay corners, Snap Curves To
Lines levels them. The old Douglas-Peucker and simplify fitter, and the crate's pathops dependency, go.
Outline on the thin-line inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- painted outline 0.310 -> 0.055 px off on average; 81 -> 14 anchors for five lines
- centre line 0.295 -> 0.052 px from the true centre line; stroke width 0.13 -> 0.02 px off; 18.4 -> 2.7
anchors a stroke (blurred, noisy and scanned lines: 2.0 each; aliased: 4.6)
- largest distance 1.84 -> 2.94 px: the square ends of a 10 px line under a round cap
Presets without Create: Strokes are unchanged.
The documented option "replaces slightly curved lines with straight lines and snaps lines near 0 or 90 degrees
to absolute 0 or 90 degrees" (helpx, Image Trace panel options); ours did the first half only.
- With Snap Curves To Lines, a straight piece at least 2 px long and within 2.5 degrees of level or upright is
made exactly so, by moving its ends across it to their mean (the page gives no angle: 2.5 degrees is our
choice). The pieces next to a moved end follow it.
- A junction other regions share stays where it is, so abutting regions still have one curve along their edge;
a line between a junction and a free end is levelled to the junction.
- The harness gains askew inputs (a rectangle, a plus sign and two lines, 1 to 2 degrees off level and upright)
and an "upright %" column: the share of the outline length that is exactly level or upright.
On the clean askew inputs (docs/image-trace-quality.md): Black and White Logo and Technical Drawing, the presets
with the option on, go from 0% to 91% and 95% of their outline exactly level or upright. Their outlines are then
0.49 and 0.59 px from the art as drawn where they were 0.05 (4.2 px at the far end of a 300 px side turned 1.5
degrees): that distance is what the option is for. Presets without the option are unchanged.
Against the documented panel (https://helpx.adobe.com/illustrator/desktop/manage-objects/traces-mockups-symbols/image-trace-panel-options.html):
- Ignore Color: "Ignores a specific color while tracing. Use the color picker to selectively ignore a color."
The panel's Ignore White is now Ignore Color with a colour button beside it (white until another colour is
picked); `imageTrace.make` takes `ignoreColor: "#rrggbb"` beside `ignoreWhite`, and leaves out the palette
colours within about 30 levels of it. Documents saved before have no such setting and ignore white as they
did. Flat Logo mode leaves out white only.
- Auto Color ("Creates a posterized image from a photo or artwork"): Color mode with the Automatic palette.
- Outline ("Simplifies the image to black outlines"): Black and White with Create: Strokes and no fills.
- The Outline preset's name is translated as a preset's name, not as the Outline view's.
Measured (docs/image-trace-quality.md): Auto Color on flat art is 0.140 px off on average with 4.0 paths (16
Colors: 0.141, 4.2). Outline on the line inputs, the first measure of Create: Strokes: 0.310 px off on average,
1.84 at worst, 81 anchors for 5 lines (Line Art's filled outlines: 0.055, 0.96, 46).
Black and White read every pixel as a blend of "black" and "white", and took for those the mean luminance of
the image's black and white pixels. In blurred or scanned line art most black pixels are part paper, so the
mean black was a gray: the middle of every line counted as more than all ink, and by how much changed as the
line crossed the pixel rows, which put a ripple on its edges that the fit then followed with anchors.
- Black is the image's darkest black (the 2nd percentile of its black pixels' luminance).
- White is the lightest pixel within a few pixels of each crack: the paper as it is there. A scan's paper is
darker in one corner than in another, and read against the image's lightest white it counted as part ink.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- Line Art: 78 -> 46 anchors, outlines 0.093 -> 0.055 px off on average (blurred lines 168 -> 53 anchors,
scanned 199 -> 70); before sub-pixel edges it was 25 anchors and 0.158 px off
- Technical Drawing: 56 -> 46 anchors, 0.092 -> 0.084 px off
- Sketched Art: 0.197 -> 0.186 px off; Default 0.092 -> 0.090; Black and White Logo 0.063 -> 0.059 with
27 -> 29 anchors
Not kept: reading lines up to six pixels deep by their ink's centroid and width, and a looser tolerance for
straight runs, neither of which measured better.
Every colour layer took a mask, component labels, a fill stack and an edge map the size of the whole image,
and as many layers were traced at once as the machine has cores.
- A layer is traced within the box its pixels lie in.
- The stack that fills components holds `u32` indices (a mask has at most 64 million pixels).
- Layers are traced as many at a time as fit in half a gigabyte (about ten bytes a pixel of the largest
layer's box each), on however many cores.
Peak memory above the image itself, photo-like image (docs/image-trace-quality.md), before -> after:
- 16 megapixels: High Fidelity Photo 3,856 -> 880 MB (2.85 -> 3.65 s), Low Fidelity Photo 1,972 -> 754 MB
(1.49 -> 1.80 s), 16 Colors 1,625 -> 298 MB, Shades of Gray 852 -> 407 MB, Default 256 -> 199 MB
- 4 megapixels: High Fidelity Photo 981 -> 643 MB, 16 Colors 408 -> 122 MB, times unchanged
The traces are the same, path for path.
Each region's outline was fitted on its own, so the edge between two regions was fitted twice, a little
differently, and left hairline gaps and overlaps.
- An outline is cut at its junctions: the pixel corners where three or more regions meet, where two parts of a
region touch by a corner only, and where an edge reaches the image's border (each side of the image is a
neighbour of its own, so the image's corners stay exact). A junction lies where the edges around it say, the
same for every region around it.
- Each piece between two junctions is the whole edge between two regions. Both get exactly the same points for
it (shifts are rounded to 1/1024 px so that the two sides agree to the last bit; whether a piece is hard is
decided by the piece alone) and it is fitted the same way from either side (from its end further left), so it
is one and the same curve in both paths. A loop without junctions is fitted clockwise from its leftmost point:
a shape's outline and the hole it leaves in the shape around it are one curve too.
- Stacked layers (Overlapping) share no edges and are cut at the image's border only.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- Default: gaps 22.2 -> 0.8 px, overlaps 22.4 -> 0.5 px
- 3 Colors: gaps 48.6 -> 0.0, overlaps 29.4 -> 0.0; outlines 0.087 -> 0.104 px off on average
- 6 Colors: gaps 39.0 -> 0.2, overlaps 35.7 -> 0.3; 0.137 -> 0.140 px off, largest 1.09 -> 1.34
- 16 Colors: gaps 34.5 -> 0.2, overlaps 26.4 -> 0.2; 0.133 -> 0.141 px off, largest 1.09 -> 1.31
A photo's noise is as large as the step from one palette colour to the next, so noise decided pixel by pixel
which of two neighbouring colours a pixel got: tens of thousands of specks, or (since the palette change)
neighbouring tones merged into one.
- A continuous-tone image (eight colours leave much of it unsaid; flat art, however noisy or unevenly lit, is
not one) is smoothed before it is quantised: three rounds of a small bilateral filter, which averages noise
away within a tone and keeps the edges between tones where and as sharp as they were.
- With Method: Overlapping, layers are stacked by lightness, from the largest colour's end of the scale,
instead of by area. Each layer reaches under those above it, so where two colours meet every layer between
them in the stack ends on that same edge and shows through its anti-aliasing: by area that was an unrelated
colour's hairline around every region; by lightness it is a neighbouring tone.
- Ignore White with Overlapping: no layer reaches under the white that is left out.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- High Fidelity Photo: colour error 2.37 -> 1.75 (2.30 at the baseline), edge error 2.59 -> 1.98, 639 -> 121
paths (3,653 at the baseline), 25,604 -> 9,818 anchors, specks 152 -> 10; a 16 megapixel photo-like image is
traced in 3.5 s (31,131 paths) where it was refused
- Low Fidelity Photo: colour error 2.67 -> 2.45, 55 -> 37 paths
- Shades of Gray: 73 -> 17 paths, colour error 9.33 -> 9.26
- The other presets' numbers are unchanged
Color and Grayscale chose their colours from every pixel, so the blends along anti-aliased edges took palette
entries and traced as slivers, and with more colours asked for than the art has, k-means split flat colours
along their noise and the halves traced as specks all over each other.
- The palette is made from the picture's own colours: a pixel that lies between the pixels on opposite sides
of it is a blend and counts for nothing (lines one pixel wide and noise are no blends).
- Colours that noise made of one colour merge: close colours whose pixels are mixed through each other. The
bands of a gradient keep to themselves and stay apart.
- A blend pixel whose nearest palette colour is a third colour (halfway from navy to yellow lies an olive that
is nearer to a green elsewhere) goes to the nearer of the two colours it lies between.
- Boxes are cut where their two sides differ most (Otsu's criterion) instead of at the median, which split the
largest colour of flat art along its noise and left two smaller colours in one box.
- Colours are compared in Oklab when pixels are assigned and in k-means.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md), before -> after:
- 16 Colors: 69.9 -> 4.2 paths, 1743 -> 66 anchors, outlines 5.08 -> 0.13 px off on average (largest 85.9 ->
1.09), kinks 1376 -> 4.4, paths in a colour the art doesn't have 5.9 -> 0
- 6 Colors: 21.2 -> 4.0 paths, 4.44 -> 0.14 px off; 3 Colors: colour error 4.86 -> 0.43, 0.33 -> 0.09 px off
- High Fidelity Photo: 3636 -> 639 paths, 81,597 -> 25,604 anchors, colour error 2.50 -> 2.37; a 1 megapixel
photo-like image 1.98 -> 0.42 s (51,389 -> 4,298 paths), a 4 megapixel one traced (27,583 paths) where it was
refused
- Low Fidelity Photo: 128 -> 55 paths, colour error 2.59 -> 2.67; Shades of Gray: 91 -> 73 paths, 9.29 -> 9.33
Each crack between an inside and an outside pixel is moved to where the pixels across it say the edge is (the
blend of the two tones in the column of pixels across the crack; a thin line by the centroid and sum of its
tone; hard-edged images are read as staircases), and the outline is fitted as Flat Logo mode fits its own:
corners put back, straight runs as lines, a round outline as a circle, the rest as few curves as Paths allows.
Snap Curves To Lines straightens slightly curved runs and makes arcs. A fit that strays from its outline
gives way to a plainer one, and at last to the outline's own points.
On each preset's own inputs, all sizes and variants (docs/image-trace-quality.md):
- Default: outlines 0.313 -> 0.091 px off on average, largest 1.51 -> 1.02; edge error 17.2 -> 10.1;
gaps between abutting paths 63.5 -> 22.2 px, overlaps 67.0 -> 22.4 px
- Black and White Logo: 0.270 -> 0.064 px off, kinks 15.3 -> 0.3, anchors 3.78 -> 2.73 times the art's
- Technical Drawing: 0.201 -> 0.086 px off; Line Art: 0.158 -> 0.093
- Worse: anchors on blurred and scanned thin lines (Line Art 25 -> 77 on average), High Fidelity Photo
(colour error 2.30 -> 2.50, anchors 46,866 -> 81,597, 1 megapixel photo-like image 0.37 -> 1.98 s)
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